When the xHCI driver needs to clean up memory (perhaps due to a failedregister restore on resume from S3 or resume from S4), it needs to resetthe number of reserved TRBs on the command ring to zero. Otherwise,several resume cycles (about 30) with a UAS device attached willcontinually increment the number of reserved TRBs, until all commandsubmissions fail because there isn't enough room on the command ring.

This patch should be backported to kernels as old as 2.6.32,that contain the commit 913a8a344ffcaf0b4a586d6662a2c66a7106557d"USB: xhci: Change how xHCI commands are handled."